The appeals court warned companies against relying on “creative lawyering that provides indefensible answers.” Liability, the appeals court said, could stem from a company’s “deliberate failure to determine the extent of its obligations.”

Relying on implausible interpretations of its obligations may constitute reckless disregard for the law and therefore amount to a willful violation, the appeals court said.

The Supreme Court adopted a notification requirement favored by the insurance companies. The standard limits the circumstances in which customers must be told their premiums are higher because of their credit ratings.

Geico did not owe a prospective customer such notification, the court said. The company had offered him a rate that was the one he would have received if his credit score had not been taken into account.

Safeco did not notify two of its customers because it thought the law did not apply to initial applications, a mistake that left the company in violation of the law.

“The company was not reckless in falling down on its duty,” Souter wrote.

Under the appeals court standard, Safeco would be required to send adverse action notices to 80 percent of the company’s new customers, Maureen Mahoney, an attorney defending the two companies, said at arguments in the Supreme Court in January. At Geico, just 10 percent of new customers qualify for the top tier of credit, Mahoney added.